For the floor of the cockpit I used some 19mm particle board I already had, plus some 44×44 mm Wood beams from the store.
I decided to make four panels and connect them, their size is 50x140cm.
That way they can be moved and handled easier than a giant piece of wood.

The raised design allows me to connect the elements nicely and makes it easy to connect parts with bolts that go through the floor.
Additionally I can run cables below if I ever decide to do that.
I applied a base coat and added carpet material to protect the Workshop floor.